Electric cartridge fuse having plug terminals

ABSTRACT

An electric fuse has a casing which is closed by terminal plugs having a relatively large axially extending internally screwthreaded bore. A screw closing the bore has an axially extending bore of relatively small diameter which houses a spring-biased blown fuse indicator mechanism.

United States Patent Inventor Richard A. Belcher Hampton Falls, N.l-l.

App]. No. 35,465

Filed May 7, 1970 Patented Nov. 16, 1971 Assignee The Chase-Shawmut Company Newburyport, Mass.

ELECTRIC CARTRIDGE FUSE HAVING PLUG TERMINALS 7 Claims, 4 Drawing Figs.

US. Cl 337/244, 3 37/276 Int. Cl H0 lh 85/30 Field oiSearch 337/148,

Primary Examiner-Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorney-Erwin Salzer ABSTRACT: An electric fuse has a casing which is closed by terminal plugs having a relatively large axially extending internally screw-threaded bore. A screw closing the bore has an ax' ially extending bore of relatively small diameter which houses a spring-biased blown fuse indicator mechanism.

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ELECTRIC CARTRIDGE FUSE HAVING PLUG TERMINALS BACKGROUND OF INVENTION In electric fuses whose tubular casing is closed by a pair of terminal plugs the latter must have several axial bores or axially extending bores. It is desired to provide terminal plugs with centrally arranged bores of relatively large diameter to shorten as much as possible the time required for filling the casing with a pulverulent arc-quenching filler, such as quartz sand. The assembly method disclosed and claimed in US. Pat. 2,740,187 to P. C. Jacobs, Jr. et al.; Apr. 3, 1956, for METHODS OF ASSEMBLING FUSES calls for the provision of central bores of relatively wide diameter in the terminal plugs of the fuses if the terminal plugs involve a relatively large mass, or are spaced relatively far apart, such as in fuses having high current ratings, or high voltage ratings. If the fuses are intended to be provided with a spring-biased blown fuse indicator pin an axial bore of relatively small diameter ought to be provided in the center of one of the terminal plugs to arrange the blown fuse indicator mechanism therein.

It is apparent'that the above requirements are inherently incompatible since it is impossible to provide in the center of a terminal plug a bore whose diameter is relatively large and at the same time relatively small. Because of the apparent incompatibility of both aforementioned requirements prior art designs are predicated on compromises between both conflicting requirements. In one compromise class of fuses a relatively large filing hole is arranged off the center of a terminal plug and a much smaller axial hole for receiving the spring-biased blown fuse indicator mechanism is arranged as its center. This compromise solution has serious drawbacks and limitations because the filling process cannot be carried out most effectively if the filling hole in a plug terminal is off center. In another compromise class of fuses a relatively large filling hole is arranged at the center of a terminal plug, and a much smaller axial hole for receiving the spring-biased blown fuse indicator mechanism is arranged off center. This second compromise solution has likewise serious drawbacks and limitations. The offcenter arrangement of the blown fuse indicator may impair the visibility of the indicating pin thereof. It further affects the entire internal design of the fuse because it precludes the arrangement of the restraining wire of the blown fuse indicator at the location where it ought to be, i.e., along the center axis of the fuse.

The present invention does away with the drawbacks and limitations of the aforementioned compromise classes of fuses.

A certain type of fuses which include internal terminal plugs are provided, in addition to the latter, with external terminal caps. These terminal caps are intended to be engaged by the contacts of a fuse holder into which the particular fuse is inserted. The internal terminal plugs must be conductively connected with the external terminal caps. The invention provides a solution to this problem which is particularly desirable as will be explained below more in detail.

SUMMARY OF THE INVENTION In fuses embodying this invention at least one of the two terminal plugs closing the casing has a centrally located internally screw-threaded axially extending bore of relatively large diameter. A screw inserted into said bore and closing said bore has an axially extending bore of relatively small diameter. A spring-biased blown fuse indicator mechanism is arranged in the last mentioned bore.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is partly a longitudinal section of a highvoltage fuse embodying the present invention, some parts of the structure being shown in elevation rather than in section, and the center portion of the fuse structure being broken away;

FIG. 2 is an end view of the structure of FIG. I; and

FIG. 3 and FIG. 4 are longitudinal sections of details of the structure of FIG. 1 drawn on a much larger scale then FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION Reference numeral 1 has been applied to indicate a tubular casing of a dimensionally stable insulating material closed on the ends thereof by metallic terminal plugs 2. Terminal plugs 2 are press fitted into casing 1 and firmly held in position by transverse or radially extending steel pins 3 projecting through casing 1 into terminal plugs 2. Terminal plugs 2 are provided at the axially inner end surfaces thereof with grooves 20 into which the axially outer ends of link-supporting insulating plates 4 are inserted. The insulating plates 4 are angularly displaced, and there are preferably four insulating plates inside of casing 1 whose planes enclose angles of 90. Insulating plates 4 form a mandrel supporting ribbon fuse links 5 of silver which are wound helically around plates 4. The axially outer ends of ribbon fuse links 5 are clamped by screws 6 against the axially inner end surfaces of terminal plugs 2. The above structure is in essence the same as that disclosed and claimed in the US. Pat. application of Frederick J. Kozacka, filed Nov. 13, I969, Ser. No. 876,445 for HIGH-VOLTAGE FUSE. A body of pulverulent arc-quenching filler 7 inside of casing l surrounds the fuse links or fusible element means 5 and insulating plates 4. One of terminal plugs 2 has an internally screw-threaded axially extending bore 2b of relatively large diameter. Screw 8 inserted into bore 2b has an axially extending bore of relatively small diameter. A spring-biased blown fuse indicator mechanism generally indicated by reference character 9 is arranged inside of relatively small diameter bore 8a. The fuse further includes a pair of terminal caps 10 each arranged at one end of casing l and overlapping one end of casing 1. Screw 9 projects through a central aperture 10a in the end surface 10b of terminal cap 10 immediately adjacent to it and screw 8 is provided with a lateral flange 8b on the axially outer end thereof clamping the end surface of one of terminal caps 10 against the axially outer end surface of the terminal plug 2 which is covered by it. This establishes a very good electrical connection between the terminal plug 2 and the terminal cap 10 which are clamped against each other by flange 8b of screw 8. The flange 8b of screw 8 has a circumference in the shape of polygon, preferably that of a hexagon, which makes it easy to tighten screw 8 by means of a wrench or like tool. A pin, preferably a roll pin 11, projects through an eccentric bore in flange 8b of screw 8 into the adjacent terminal plug, thus preventing screw 8 from getting loose.

The blown fuse indicator mechanism generally designated by reference character 9 includes spring housing 9a which is in the shape of a cap arranged inside bore 8a adjacent the axially outer end thereof, and a sealing cap 9b inside bore 80 arranged adjacent the axially inner end of bore 80. The blown fuse indicator mechanism further includes a helical spring 9c inside of spring housing and indicator pin 9d biased axially outwardly by spring 90. The sealing cap 9a has a central bore of sufficiently small diameter to preclude penetration of arcquenching filler into bore 8a. An indicator-pin-restraining wire 12 is arranged inside of bore 8a. Bore 80 forms a thermal chamber, i.e., a chamber minimizing heat flow away from indicator-pin-restraining wire 12. Therefore, when wire 12 carries current a point of high temperature along wire 12 is formed between spring housing 9a and sealing cap 9b. Initial fusion of wire 12 and are initiation takes place inside of bore 8a and thereupon wire 12 burns back until the arc is extinguished and the circuit through wire 12 interrupted. Wire 12 extends outside of bore 8a and its left end (as seen in FIG. 1) is attached to, and conductively connected with, left terminal plug 2. To this end said terminal plug 2 is provided with a relatively large internally screw-threaded central bore 2b receiving hex-screw 8' having a relatively small bore 8a into which one endof wire 12 extends and in which said one end of wire 12 is firmly clamped by metallic clamping cap 912.

Fuse links 5 and wire 12 establish parallel current paths between terminal plugs 2. The resistance of wire 12 is much larger than that of fuse links 5 and, therefore, wire 12 does not carry any significant current before fusion and vaporization of fuse links 5 takes place. Then indicator-pin-restraining wire 12 becomes current carrying and develops a hot spot at the section thereof situated inside of bore 8a. Upon fusion of wire 12 at the point where its hot spot is located indicator pin 9d is instantly free to be spring propelled axially outwardly to the indicating position thereof. In other words, the friction between pulverulent arc-quenching tiller 7 and the portion of wire 12 outside bore 8a has no adverse effect upon the operation of the blown fuse indicator mechanism of the fuse.

Hex-screw 8' projects a central aperture 10a in the left cap 10 (as seen in FIG. 1) and clamps with its flange 8b the end surface of said left cap 10 against the adjacent end surface on left tenninal plug 2. A pin 11' projects through the flange of hex-screw 8' into left terminal plug 2 to preclude any rotation of hex-screw 8' relative to left terminal plug 2.

I claim as my invention:

1. An electric fuse including in combination:

a. fusible element means having axially outer ends;

b. a body of pulverulent arc-quenching filler surrounding said fusible element means;

c. a tubular casing of insulating material, housing said fusible element means and said body of filler; a pair of terminal plugs inserted into the ends of said casing each conductively connected to one of said axially outer ends of said fusible element means, one of said axially pair of terminal plugs having a centrally located internally screw-threaded axially extending bore of relatively large diameter;

. a screw inserted into said bore and closing said bore, said screw having an axially extending bore of relatively small diameter; and a spring-biased blown fuse indicator mechanism arranged inside said bore of relatively small diameter.

. An electric fuse as specified in claim 1 including:

a pair of terminal caps each arranged at one end of said casing and overlapping one end of said casing, at least one of said pair of terminal caps having a central aperture in the end surface thereof; and

b. a lateral flange on the axially outer end of said screw clamping the end surface of said one of said pair of terminal caps against the axially outer end surface of said one of said pair of terminal plugs.

3. An electric fuse as specified in claim 2 wherein said flange has a circumference in the shape of a polygon and has an eccentric axially extending bore, and wherein a pin projects through said eccentric bore into said one of said pair of terminal plugs.

4. An electric fuse as specified in claim 1 including:

a. a pair of terminal caps each arranged at one end of said casing and overlapping one end of said casing, each of said pair of terminal caps having a central aperture in the end surface thereof;

b. a lateral flange on said axially outer end of said screw clamping the end surface of one of said pair of terminal caps against the axially outer end surface of one of said pair of terminal plugs; and

c. an additional screw having a lateral flange projecting with the shank portion thereof through said central aperture in the other of said pair of terminal caps into an internally screw-threaded axially extending bore in the other of said pair of terminal plugs and clamping with said lateral flange thereof the end surface of the other of said pair of terminal caps' against the axially outer end surface of the other of said pair of terminal plugs.

5. An electric fuse as specified in claim 4 wherein said flange of said screw and said flange of said additional screw each are in the shape of a polygon each having an eccentric axially extending bore, and wherein one of a pair of pins projects through said eccentric bore in said flange of said screw into one of said pair of terminal plugs and the other of said pair of pins projects through said flange of said additional screw into the other of said pair of terminal plu s.

6. An electric fuse as specified in claim wherein said blown fuse indicator mechanism includes a spring housing arranged inside said bore of relatively small diameter of said screw adjacent the axially outer end thereof, a sealing cap inside said bore of relatively small diameter of said screw arranged adjacent the axially inner end thereof, a helical spring inside said spring housing and an indicator pin biased by said spring and an indicator-pin-restraining wire arranged inside said bore of relatively small diameter of said screw, and wherein said bore of relatively small diameter of said screw thermally insulates a predetermined length of said indicatorpin-restraining wire to establish a point of high temperature on said indicator-pin-restraining wire when carrying current situated between said spring housing and said sealing cap.

7. An electric fuse including in combination:

a. fusible element means having axially outer ends;

b. a body of pulverulent arc-quenching filler surrounding said fusible element means;

c. a tubular casing of insulating material housing said fusible element means and said body of filler;

d. a pair of terminal plugs inserted into the ends of said casing each conductively connected to one of said axially outer ends of said fusible element means, each of said pair of terminal plugs having a centrally located internally screw-threaded axially extending bore of relatively large diameter;

e. a pair of terminal caps each arranged at one end of said casing and overlapping one end of said casing, each of said pair of terminal caps having a central aperture in the end surface thereof;

f. a pair of screw plugs each having a shank portion projecting through said central aperture in the end surface of one of said pair of terminal caps into said bore of relatively large diameter of one of said pair of terminal plugs and each of said pair of screw plugs having an axially outer flange portion abutting against the axially outer end surface of one of said air of terminal caps and clamping the end surface of one of said pair of terminal caps against an axially outer end surface of one of said pair of terminal plugs, each of said pair of screw plugs having an axially extending bore of relatively small diameter;

. a blown fuse indicator restraining wire inside said casing having axially outer ends each projecting into said bore of relatively small diameter of one of said pair of screw plugs;

h. a restraining wire clamping means for one of said axially outer ends of said restraining wire; and

i. a spring-biased blown fuse indicator mechanism arranged inside said bore of relatively small diameter of one of said pair of screw plugs and normally restraining wire. 

1. An electric fuse including in combination: a. fusible element means having axially outer ends; b. a body of pulverulent arc-quenching filler surrounding said fusible element means; c. a tubular casing of insulating material, housing said fusible element means and said body of filler; d. a pair of terminal plugs inserted into the ends of said casing each conductively connected to one of said axially outer ends of said fusible element means, one of said axially pair of terminal plugs having a centrally located internally screwthreaded axially extending bore of relatively large diameter; e. a screw inserted into said bore and closing said bore, said screw having an axially extending bore of relatively small diameter; and f. a spring-biased blown fuse indicator mechanism arranged inside said bore of relatively small diameter.
 2. An electric fuse as specified in claim 1 including: a. a pair of terminal caps each arranged at one end of said casing and overlapping one end of said casing, at least one of said pair of terminal caps having a central aperture in the end surface thereof; and b. a lateral flange on the axially outer end of said screw clamping the end surface of said one of said pair of terminal caps against the axially outer end surface of said one of said pair of terminal plugs.
 3. An electric fuse as specified in claim 2 wherein said flange has a circumference in the shape of a polygon and has an eccentric axially extending Bore, and wherein a pin projects through said eccentric bore into said one of said pair of terminal plugs.
 4. An electric fuse as specified in claim 1 including: a. a pair of terminal caps each arranged at one end of said casing and overlapping one end of said casing, each of said pair of terminal caps having a central aperture in the end surface thereof; b. a lateral flange on said axially outer end of said screw clamping the end surface of one of said pair of terminal caps against the axially outer end surface of one of said pair of terminal plugs; and c. an additional screw having a lateral flange projecting with the shank portion thereof through said central aperture in the other of said pair of terminal caps into an internally screw-threaded axially extending bore in the other of said pair of terminal plugs and clamping with said lateral flange thereof the end surface of the other of said pair of terminal caps against the axially outer end surface of the other of said pair of terminal plugs.
 5. An electric fuse as specified in claim 4 wherein said flange of said screw and said flange of said additional screw each are in the shape of a polygon each having an eccentric axially extending bore, and wherein one of a pair of pins projects through said eccentric bore in said flange of said screw into one of said pair of terminal plugs and the other of said pair of pins projects through said flange of said additional screw into the other of said pair of terminal plugs.
 6. An electric fuse as specified in claim 1 wherein said blown fuse indicator mechanism includes a spring housing arranged inside said bore of relatively small diameter of said screw adjacent the axially outer end thereof, a sealing cap inside said bore of relatively small diameter of said screw arranged adjacent the axially inner end thereof, a helical spring inside said spring housing and an indicator pin biased by said spring and an indicator-pin-restraining wire arranged inside said bore of relatively small diameter of said screw, and wherein said bore of relatively small diameter of said screw thermally insulates a predetermined length of said indicator-pin-restraining wire to establish a point of high temperature on said indicator-pin-restraining wire when carrying current situated between said spring housing and said sealing cap.
 7. An electric fuse including in combination: a. fusible element means having axially outer ends; b. a body of pulverulent arc-quenching filler surrounding said fusible element means; c. a tubular casing of insulating material housing said fusible element means and said body of filler; d. a pair of terminal plugs inserted into the ends of said casing each conductively connected to one of said axially outer ends of said fusible element means, each of said pair of terminal plugs having a centrally located internally screw-threaded axially extending bore of relatively large diameter; e. a pair of terminal caps each arranged at one end of said casing and overlapping one end of said casing, each of said pair of terminal caps having a central aperture in the end surface thereof; f. a pair of screw plugs each having a shank portion projecting through said central aperture in the end surface of one of said pair of terminal caps into said bore of relatively large diameter of one of said pair of terminal plugs and each of said pair of screw plugs having an axially outer flange portion abutting against the axially outer end surface of one of said pair of terminal caps and clamping the end surface of one of said pair of terminal caps against an axially outer end surface of one of said pair of terminal plugs, each of said pair of screw plugs having an axially extending bore of relatively small diameter; g. a blown fuse indicator restraining wire inside said casing having axially outer ends each projecting into said bore of relatively small diameter of one of said pair of screw plugs; h. a restraining wire clamping means for one oF said axially outer ends of said restraining wire; and i. a spring-biased blown fuse indicator mechanism arranged inside said bore of relatively small diameter of one of said pair of screw plugs and normally restraining wire. 